Boris Lakard

Ammonia gas sensor based on electrosynthesized polypyrrole films.

In this work, design and fabrication of micro-gas-sensors, polymerization and deposition of poly(pyrrole) thin films as sensitive layer for the micro-gas-sensors by electrochemical processing, and characterization of the polymer films by FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), are reported. The change in conductance of thin polymer layers is used as a sensor signal. The behaviours, including sensitivity, reproducibility and reversibility, to various ammonia gas concentrations ranging from 8 ppm to 1000 ppm are investigated. The influence of the temperature on the electrical response of the sensors is also studied. The experimental results show that these ammonia gas sensors are efficient since they are sensitive to ammonia, reversible and reproducible at room temperature.

Urea potentiometric enzymatic biosensor based on charged biopolymers and electrodeposited polyaniline

A potentiometric biosensor based on urease was developed for the quantitative determination of urea concentration in aqueous solutions for biomedical applications. The urease was either physisorbed onto an electrodeposited polyaniline film (PANI), or immobilized on a layer-by-layer film (LbL) assembled over the PANI film, that was obtained by the alternate deposition of charged polysaccharides (carboxymethylpullulan (CMP) and chitosan (CHI)). In the latter case, the urease (Urs) enzyme was either physically adsorbed or covalently grafted to the LbL film using carbodiimide coupling reaction. Potentiometric responses of the enzymatic biosensors were measured as a function of the urea concentration in aqueous solutions (from 10(-6) to 10(-1) mol L(-1) urea). Very high sensitivity and short response time were observed for the present biosensor. Moreover, a stability study showed a higher stability over time for the potentiometric response of the sensor with the enzyme-grafted LbL film, testifying for the protective nature of the polysaccharide coating and the interest of covalent grafting.

Miniaturized pH biosensors based on electrochemically modified electrodes with biocompatible polymers.

Potentiometric pH sensors based on linear polyethylenimine (L-PEI) and linear polypropylenimine(L-PPI), two synthetic enzymes and biocompatible polymers, films were prepared by electropolymerization of three different monomers: ethylenediamine (EDA), 1,3-diaminopropane (1,3-DAP) and diethylenetriamine (DETA) in order to be used in clinical, dermatological and biological applications, such as in vivo analysis. In a first step a biosensor was tested which consisted in a platinum wire protruded from glass sheath. The polymer film coated on these platinum electrodes showed good linear potentiometric responses to pH changes from pH 3 to 10. Resulting electrodes present both good reversibility and good stability versus time. The effect of the different polymer film thicknesses to potentiometric responses was also studied. This study allowed us to develop a miniaturized pH biosensor in the second step. This sensor was fabricated using photo-lithography, followed by sputtering and lift-off processes, and it included an electronic detection system. We have also successfully studied the potentiometric responses to pH changes of this device over a period of 1 month, and so we propose this new pH micro-biosensor as an alternative to classical pH sensors currently used in dermatology.

Effect of ultrasounds on the electrochemical synthesis of polypyrrole, application to the adhesion and growth of biological cells.

In this study, a new way to synthesize polypyrrole films is presented. This original way consists in the electropolymerization of polypyrrole under high frequency ultrasonic irradiation on conductive fluorine-doped tin oxide surfaces. The polypyrrole films obtained are then compared, in terms of chemical structure and morphology, to polypyrrole films synthesized by standard electrochemical methodology. Next, these polymer films are tested as an alternative to biomaterials that are commonly used as cell culture substrates. Thus, the adhesion and growth of osteoblastics cells and microbial cells on polymer-modified surfaces are investigated by using qualitative observation and quantitative tests. These studies proved the non-toxicity of the polymer films for osteoblastic and microbial cells but also a different behaviour of osteoblastic cells and microbial cells with polypyrrole films.

pH Sensing at Pt Electrode Surfaces Coated with Linear Polyethylenimine from Anodic Polymerization of Ethylenediamine

A novel pH sensor using a smooth Pt electrode coated with an electrically insulating polymer is addressed in this study. We present a new electrochemically modified Pt electrode. Its modification results from the anodic oxidation of pure ethylenediamine, charged with lithium trifluoromethanesulfonate, which leads to the formation of a polymer coating in one step. The assembly of the electrode surface coated with electropolymerized ethylenediamine acts as a transducer of the electrode potential vs. the pH value in aqueous solutions. It has been shown that the anodic oxidation of pure ethylenediamine yields polyethylenimine which is a high impedance polymer containing amino groups sensitive to H + concentration. Since the reproducibility of polymer-based pH sensors is a controversial subject, we examined both the effect of the electrode-bias time, which can be linked to the polymer thickness, and the aging of the polymer on the potentiometric response of the sensor. The pH sensor we propose here has a quasi-Nernstian behavior. It is reliable for some weeks in the pH range from 3 to 11 in aqueous media.

Ab initio study of the polymerization mechanism of poly(p-phenylenediamine)

The electrochemical oxidation of paraphenylenediamine (1,4-diaminobenzene, PPD) leads to the passivation of the electrode surface by a thin film as shown by using Cyclic Voltammetry technique. This film can be identified by InfraRed-Attenuated Total Reflectance as a polymeric film of poly(p-phenylenediamine), polyPPD. To establish the mechanism leading from PPD to polyPPD, we performed computations of energy and thermochemical values with the quantum-chemical Self-Consistent Field method at the Hartree–Fock level of theory. Then we compared this mechanism to the ones, previously established with similar ab initio calculations, leading to polyethyleneimine and polypropyleneimine in an attempt to generalize the mechanism of electropolymerization of diamines.

Adsorption of Ni(II) ions on colloidal hybrid organic-inorganic silica composites.

Two new silica-based composites were prepared as adsorbents for the capture of Ni(II) ions. The first strategy consists in coating chitosan on colloidal fumed silica after acidic treatment yielding the composite SiO(2)+CS. The second route involves in a first step surface condensation of triethoxysilylbutyronitrile, followed by acidic hydrolysis of the surface-bound nitrile groups affording silica particles covered by carboxylic group. In a third step, chitosan has been grafted on the surface-bound C(=O)OH groups yielding the composite SiO(2)(CO(2)H)+CS. The novel hybrid materials were characterized by IR spectroscopy, scanning electron and AFM microscopy, and zeta potential measurements. Batch experiments were conducted to study the sorption performance of these composites for Ni(II) removal from aqueous NiCl(2) solution at different pH. Both Langmuir, Freundlich, and Temkin isotherm models provide good fits with the experimental data. It was shown that these low-cost materials present a promising capacity to adsorb Ni(II) ions. At pH 7, the maximum adsorption capacity q(max)of Ni(II) on the adsorbent, is found to be 182 mg g(-1) for SiO(2)+CS, and 210 mg g(-1) for SiO(2)(CO(2)H)+CS.

Charge properties of membranes modified by multilayer polyelectrolyte adsorption.

Alternate adsorption of polyanions and polycations on a polyethersulfone (PES) membrane was studied by the tangential streaming potential method using a parallel-plate channel to investigate the properties of the outer surface of the membrane. These streaming potential data were complemented by diffusion experiments and by membrane potential measurements in order to characterize the inner surface of the membrane. Tangential streaming potential measurements demonstrated that after completing a bilayer of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrene sulfonate) (PSS), periodic variations in the zeta potential between positive and negative values appeared for multilayer films obtained from membrane dipped in polyelectrolyte (PE) solutions at 10 g/L. On the contrary, the zeta potential was always positive when multilayer films were obtained from 1 and 5 g/L polyelectrolyte concentration solutions. Diffusion experiments carried out with unmodified and modified membranes showed a decrease in the solute flux after functionalization of the membrane by several polyelectrolyte bilayers, indicating that the diffusional resistance of the PE layers contributes significantly to the overall resistance to diffusion of the modified membrane. By means of membrane potential measurements the pore walls of the membrane were functionalized since the charge of its pore walls was modified even if it is difficult to discriminate between the contribution of the membrane and that of the multilayer buildup.

Development of Amperometric Biosensors Based on Nanostructured Tyrosinase-Conducting Polymer Composite Electrodes

Bio-composite coatings consisting of poly(3,4-ethylenedioxythiophene) (PEDOT) and tyrosinase (Ty) were successfully electrodeposited on conventional size gold (Au) disk electrodes and microelectrode arrays using sinusoidal voltages. Electrochemical polymerization of the corresponding monomer was carried out in the presence of various Ty amounts in aqueous buffered solutions. The bio-composite coatings prepared using sinusoidal voltages and potentiostatic electrodeposition methods were compared in terms of morphology, electrochemical properties, and biocatalytic activity towards various analytes. The amperometric biosensors were tested in dopamine (DA) and catechol (CT) electroanalysis in aqueous buffered solutions. The analytical performance of the developed biosensors was investigated in terms of linear response range, detection limit, sensitivity, and repeatability. A semi-quantitative multi-analyte procedure for simultaneous determination of DA and CT was developed. The amperometric biosensor prepared using sinusoidal voltages showed much better analytical performance. The Au disk biosensor obtained by 50 mV alternating voltage amplitude displayed a linear response for DA concentrations ranging from 10 to 300 μM, with a detection limit of 4.18 μM.

Doping properties of PEDOT films electrosynthesized under high frequency ultrasound irradiation.

The present study presents the use of high frequency ultrasound (500 kHz, 25 W) for 3,4-ethylenedioxythiophene (EDOT) electropolymerization in aqueous medium in order to investigate its effects on conducting polymer properties. It was shown that mass transfer increases under ultrasound irradiation which improved electropolymerization and the comparison with experiments carried out at the same mass transfer level (4.6 × 10(-5) ms(-1)) puts in evidence that stirring effect is not the only phenomenon induced by ultrasound during electrodeposition. PEDOT films elaborated under ultrasonication present increased doping levels revealed by X-ray Photoelectron Spectroscopy (XPS) analysis, especially in the case of thick films (measured by mechanical probe), thanks to better incorporation of counter ions within polymer matrix as another consequence of mass transport improvement under ultrasound and probably film heating by wave absorption for the highest thicknesses. A dilation of the film under sonication leading to an increase in film thickness was also highlighted. Finally, a refining of the surface structure was also observed via SEM imaging.